1 Preterm birth (PTB) rates are substantially higher in the United States than in other industrialized nations, 2 and are disproportionately greater among-low income and minority women. These disparities have proven 3 difficult to ameliorate despite intensive efforts. However, recent studies indicate that a group-based model of 4 prenatal care (GPNC), CenteringPregnancy, significantly reduces PTB in low-income, minority women. 5 CenteringPregnancy is a multifaceted group intervention that integrates three aspects of prenatal care: health 6 assessment, education, and social support. However, little is known about the mechanisms by which GPNC 7 reduces PTB, since the biologic pathways leading to PTB are still incompletely understood. One well- 8 supported theory posits excessive inflammatory activity in maternal circulation and the maternal-fetal interface 9 as an etiology for PTB. Our group and others have linked adverse socioeconomic conditions and maternal 10 psychosocial functioning with circulating inflammatory biomarkers, chronic placental inflammation, and adverse 11 pregnancy outcomes. GPNC may reduce PTB by reducing systemic and placental inflammatory activity 12 through improved psychosocial functioning of women in socially disadvantaged conditions. In a pilot study, we 13 found evidence suggesting that GPNC ameliorates socioeconomic differences in placenta inflammatory lesions 14 and gene expression profiles.Though promising, replication of these results in a larger cohort is needed in 15 order to identify psychological, behavioral and biological mechanisms through which GPNC affects 16 inflammatory activity at the maternal-fetal interface,utilize placental gene expression to evaluate alternate 17 biologic pathways and to clarify the implications of these changes for reduction of PTB disparities. 18 Here, we propose to address these questions by leveraging an existing trial in Greenville, South Carolina 19 (1R01HD082311) that will enroll 3160 women from a predominantly low-income population. The parent study 20 employs a randomized controlled trial design to compare GPNC with traditional prenatal care, and is 21 adequately powered to detect differences in PTB by intervention and race. The parent study will collect and 22 analyze survey measures of behavioral and psychosocial outcomes, but it does not have the resources to 23 collect biomarkers or evaluate biologic mechanisms of action. The goal of this proposal is to add biospecimen 24 collection to the existing trial in order to understand whether GPNC, by improving psychosocial and behavioral 25 functioning, influences the inflammatory milieu during gestation. Specimens will be collected from 1150 women 26 and full analysis performed on a random subset of 900, with the aims of (1) quantifying differences in systemic 27 inflammatory biomarkers, placental histologic inflammation, and placental gene expression between women 28 participating in GPNC and those receivng routine prenatal care and (2) determining whether these differences 29 are mediated by improvements in psychosocial functioning and/or lifestyle characteristics. Ultimately, we aim to 30 understand the biological mechanisms through which GPNC reduces the frequency of PTB.